The objectives of the present research project are: 1) to understand the mechanism and control of replication of bacterial plasmids, per se, 2) to define those aspects of the mechanism and control of replication of DNA which are required for the replication of all independent genetic units (replicons) and those requirements which are specific for a particular replicon, and 3) to use information obtained with plasmids to help understand the mechanism and control of replication of the bacterial chromosome and the relationship between chromosome replication, the cell cycle, and cell division.